Crawler belt, crawler unit and method for manufacturing crawler belt

ABSTRACT

A crawler belt is disclosed herein having an endless steel belt (high-tensile-strength belt) and a belt main body made of rubber and attached around an outer periphery of the steel belt. The steel belt has engagement holes arranged at even intervals in a circumferential direction thereof. The belt main body has escape recesses formed therein. A wheel has projections arranged at even intervals in a circumferential direction on an outer peripheral surface thereof. The projections are adapted to be engaged with the engagement holes of the steel belt and at the same time to enter the escape recesses of the belt main body.

TECHNICAL FIELD

This invention relates to a crawler belt and a crawler unit used in acrawler structure of a light-weight robot, etc. and a method formanufacturing the crawler belt.

BACKGROUND ART

Rubber crawler belts to be used in a light-weight robot, etc. have beendeveloped. The crawler belts have tread lugs on outer periphery thereofand equally-spaced projections for engaging with a wheel or a sprocketon inner periphery thereof. Such crawler belts, however, tend to stretchtoo much, go slack and come off the wheel after long use. Sometimes theymay break due to lack of strength. If the crawler belts are increased inthickness to overcome these shortcomings, they are increased in weight,too.

To address the above-mentioned problem, technologies have been developedto reinforce the crawler belts by embedding an endlesshigh-tensile-strength belt made of thin metal belt, etc. in arubber-made main body of the crawler belt as disclosed in the patentdocuments 1 to 3 listed below.

Patent Document 1: Japanese Patent Application Laid-Open No. H6-156333

Patent Document 2: Japanese Patent Application Laid-Open No. H6-199253

Patent Document 3: Japanese Patent Application Laid-Open No. H6-329057

SUMMARY OF THE INVENTION

Crawler belts disclosed in the Patents Documents 1 to 3 may be enhancedin strength, but can be reduced in weight only to a limited degree dueto projections for engaging with a wheel or a sprocket.

Recently, a robot for searching and rescuing people trapped under therubble at the time of disasters such as an earthquake and otherlight-duty robots have been developed. In such light-weight robots,further reduction in weight of a crawler unit is desired. However,reinforced crawler belts as disclosed in the above-listed patentdocuments fail to meet the demand of weight reduction.

The present invention has been made in order to solve the abovementioned problem. According to the present invention, there is provideda crawler belt comprising an endless high-tensile-strength belt (21) anda belt main body (22) made of elastic material and attached to an outerperiphery of the high-tensile-strength belt, the high-tensile-strengthbelt (21) having engagement holes (21 a) arranged at even intervals in acircumferential direction thereof the belt main body (22) having escaperecesses (23 a) formed at locations corresponding to the engagementholes of the high-tensile-strength belt.

According to the present invention, there is also provided a crawlerunit comprising a plurality of wheels (10) disposed separately in afront and rear direction and a crawler belt (20) trained about thewheels, wherein

the crawler belt (20) comprises an endless high-tensile-strength belt(21) and a belt main body (22) made of elastic material and attached toan outer periphery of the high-tensile-strength belt, thehigh-tensile-strength belt (21) having engagement holes (21 a) arrangedat even intervals in a circumferential direction thereof, the belt mainbody having escape recesses (23 a) formed at locations corresponding tothe engagement holes of the high-tensile-strength belt, and wherein

a driving wheel of the plurality of wheels (10) has engagementprojections (12 a) arranged at even intervals in a circumferentialdirection on an outer peripheral surface thereof, the engagementprojections (12 a) being adapted to be engaged with the engagement holes(21 a) of the high-tensile-strength belt (21) of the crawler belt (20)and at the same time to enter the escape recesses (23 a) of the beltmain body (22).

In the crawler belt and the crawler unit as constructed above, owing tothe endless high-tensile-strength belt incorporated in the crawler belt,the crawler belt has a high tensile strength and is free fromundesirable events such as having been stretched too much and coming offthe wheel. It is free from breakage, either. Moreover, since theengagement holes are formed on the high-tensile-strength belt and theprojections of the wheel are adapted to be engaged with the engagementholes, the belt main body made of elastic material is not required tohave projections for engaging with a wheel. This further contributes tothe reduction of weight.

Preferably, outer peripheral surfaces of the plurality of wheels (10)are generally cylindrical surfaces. More preferably, the engagementholes (21 a) of the high-tensile-strength belt (21) have a generallycircular shape and the engagement projections (12 a) of the wheel (10)have a generally semi-spherical shape. This contributes to the reductionof noise.

Preferably, the crawler unit further comprises a pair of side plates(30) extending in a front and rear direction to cover opposite sidesurfaces of the plurality of wheels (10), the belt main body (22)comprising an endless base part (23) and shielding flanges (24, 24′)continuously formed along an entire length on opposite sides of the basepart, edges of the shielding flanges contacting peripheral edges of theside plates. The shielding flanges serves to shield an inner spacebetween the side plates, thus preventing foreign substances such as sandand dusts from entering between the crawler belt and the wheels.

More preferably, the shielding flange has a tapered cross-section and iselastically deformed as it contacts semi-circular peripheral edges of afront and rear end portions of the side plate. A part of the crawlerbelt which is placed around the wheel is subjected to a force to causethe edge of the shielding flange to be waved. But the edge of theshielding flange can contact the side plate securely without being wavedbecause the edge part of the shielding flange is elastically deformed asit contacts the side plates.

More preferably, upper and lower edges of the side plates locatedbetween the wheels are made of a seal member, the seal member havingsmaller elastic coefficient than the shielding flange, the seal memberbeing deformed as it contacts the edge of the shielding flange. Thispermits the shielding flange and the seal member to be securelymaintained in contact with each other even when the crawler belt flapbetween the wheels.

Preferably, the belt main body (22) includes an endless base part (23)and a plurality of tread lugs (26) formed spacedly on the outerperiphery of and extending in a width direction of the base part (23),the tread lugs having a planer shape bent at least at one point, heightof the tread lugs being not less than 3 times and not greater than 7times as large as its thickness. This enables a robot, etc. to keeprunning without slipping even if it encounters the rubble, etc. as itruns on the unleveled ground, by allowing the tread lugs to beelastically deformed and grip the rubble, etc. Moreover, although thetread lugs are high and slim, they can support the self-weight of therobot, etc. since they have bent planer shapes.

According to the present invention, there is provided a method formanufacturing a crawler belt, the method comprising steps of:

preparing a first mold (70) having a plurality of mold projections (74a) arranged at even intervals on a molding surface thereof and a secondmold (80) having a plurality of lug mold recesses (86) opening at amolding surface thereof;

setting an endless high-tensile-strength belt (21) having engagementholes (21 a) arranged at even intervals in a circumferential directionthereof on the first mold (70) by fitting the mold projections (74 a)into the engagement holes; and

molding an elastic material between the first mold and the second moldto obtain a belt main body (22) or a part (22′) of the belt main body(22) attached to an outer periphery of at least a part of thehigh-tensile-strength belt, at the same time forming escape recesses (23a) by allowing the molding projections (74 a) of the first mold (70) topress into the elastic material and forming tread lugs (26) by allowingthe elastic material to enter the lug mold recesses (86) of the secondmold (80).

In the method described above, a positioning device is not necessarybecause the engagement holes of the high-tensile-strength belt can beused as a positioning device. Moreover, the tread lugs can be moldedeasily and inexpensively because molding is accomplished by allowing theelastic material to enter the lug mold recess.

According to the present invention, there is further provided a methodfor manufacturing a crawler belt, the method comprising steps of:

preparing a lower mold (70) having a plurality of mold projections (74a) arranged at even intervals on an upper surface thereof and an uppermold (80) having a plurality of lug mold recesses (86) opening at anlower surface thereof;

positioning an endless high-tensile-strength belt (21) having engagementholes (21 a) arranged at even intervals in a circumferential directionthereof by placing a part of the high-tensile-strength belt (21) on thelower mold (70) and by fitting the mold projections (74 a) of the lowermold into the engagement holes of the high-tensile-strength belt;

placing an elastic material on said lower mold and lowering said uppermold to mold a part (22′) of a belt main body (22) on an outer peripheryof the high-tensile-strength belt (21) between the upper mold and thelower mold, at the same time forming escape recesses (23 a) by allowingthe mold projections (74 a) of the lower mold (70) to press into theelastic material, and forming tread lugs (26) by allowing the elasticmaterial to enter the lug mold recesses (86) of the upper mold (80); and

molding the endless belt main body (22) all around the periphery of thehigh-tensile-strength belt (21) by moving the high-tensile-strength belt(21), to place a new part of the high-tensile-strength belt (21) on thelower mold (70), the new part adjoining the part where the part (22′) ofthe belt main body (22) was molded, molding another part (22′) of thebelt main body on said new part of said high-tensile-strength belt inthe foregoing way, and by repeating the procedure.

In the method described above, the crawler belt can be manufacturedeasily and inexpensively without using expensive equipment. Moreover, apositioning device is not necessary because the engagement holes of thehigh-tensile-strength belt can be used as a positioning device.Moreover, the tread lugs can be molded easily and inexpensively becausemolding is accomplished by allowing the elastic material to enter thelug mold recess. Furthermore, crawler belts of various circumferentiallengths can be manufactured with the same equipment.

Preferably, mold pins (74) are removably inserted into the upper surfaceof the lower mold (70) and head parts of the mold pins are provided asthe mold projections (74 a). By this, after molding, the molded part ofthe belt main body and the high-tensile-strength belt can be removedfrom the lower mold without substantial resistance, which contributes tosignificantly improve productivity.

According to the present invention, a crawler belt with high strengthand light weight can be obtained. By using the method according to thepresent invention, a crawler belt incorporating a high-tensile-strengthbelt can be manufactured easily and inexpensively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a crawler structure of a robot having apair of left and right crawler units according to a first embodiment ofthe present invention.

FIG. 2 is a side view of the crawler unit.

FIG. 3 is a longitudinal sectional view of a crawler belt used in thecrawler unit with a thickness of a steel belt exaggerated.

FIG. 4 is a longitudinal sectional view of the crawler belt in a stateof being placed around a wheel.

FIG. 5 is a side view of the crawler belt.

FIG. 6 is a plan view of the crawler belt.

FIG. 7 is a schematic view of tread lugs of the crawler belt as they aregripping rubble.

FIG. 8 is a perspective view of equipment used for manufacturing thecrawler belt.

FIG. 9 is an enlarged longitudinal view of a main part of the equipmentshowing a belt main body of the crawler belt being molded.

FIG. 10 is an enlarged longitudinal view of a main part of the equipmentshowing a molded part of the belt main body and the steel belt beingremoved from a lower mold.

FIG. 11 is an enlarged longitudinal view of a main part of the equipmentshowing a mold pin being removed form a molded part of the belt mainbody and the steel belt.

FIG. 12 is a longitudinal sectional view of a crawler unit according toa second embodiment of the present invention.

FIG. 13 is a longitudinal sectional view of a crawler unit according toa third embodiment of the present invention.

FIG. 14 is an enlarged longitudinal sectional view of a crawler beltaccording to a fourth embodiment of the present invention.

FIG. 15 is a longitudinal sectional view showing a seal structurebetween the crawler belt and an end edge of a side plate according tothe fourth embodiment of the present invention.

FIG. 16 is a longitudinal sectional view showing a seal structurebetween the crawler belt and a middle part of the side plate accordingto the fourth embodiment of the present invention.

FIG. 17 is a perspective view of equipment used for manufacturing thecrawler belt according to the fourth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

First embodiment of the present invention is described below referringto FIGS. 1 to 11. FIG. 1 shows a crawler structure A, which constitutesa lower body of a light-duty robot. The crawler structure comprises amounting base 1 and a pair of crawler units 2 attached to the left andright of the mounting base 1. An upper body of the robot is mounted onthe mounting base 1. The upper body may be of various constructions,according to the role of the robot. For example, a robot for searchingpeople trapped under the rubble at the time of disasters such as anearthquake has a camera, a detection sensor and an illuminating device,and a grasping mechanism for grasping light-weight items, according tonecessity.

As shown in FIGS. 1 and 2, each of the crawler units 2 comprises wheels10 in the front and rear, an endless crawler belt 20 trained about thewheels 10 and a pair of side plates 30 rotatably supporting the wheels10 in the front and rear. The side plate 30 of each of crawler units 2located on an inner side is attached to the mounting base 1 at thecentral portion of the side plate 30.

The left and right crawler units 2 are substantially of the sameconstruction. In each of the crawler units 2, either one of the wheels10 in the front or in the rear is connected to an actuator (not shown)such as an electric motor provided on the side plate 30 on the innerside and serves as a driving wheel and the other of the wheels serves asa trailing wheel.

As shown in FIGS. 2 and 4, outer peripheral surface of the each of thewheels 10 is a cylindrical surface. The wheel 10 has semi-sphericalengagement projections 12 a arranged at even intervals in acircumferential direction at a center in a width direction of the outerperipheral surface thereof. In this embodiment, a diameter of theengagement projection 12 a is around 3 millimeters while a width of thewheel 10 is 30 millimeters.

As shown in FIGS. 2 and 4, the pair of side plates 30 are disposed tothe left and right of the pair of wheels 10. Each of the side plates 30is in a shape of an oblong plate elongated in a front and reardirection. Front and rear end portions of the side plates 30 coveropposite side surfaces of the pair of wheels 10. Peripheral edges offront and rear end portions of the side plates 30 are of a semi-circularshape corresponding to the shape of peripheral edges of the wheel 10.

As shown in FIG. 4, the peripheral edge of the side plate 30 has atapered cross section all around the periphery and its outer face is aninclined surface 30 c.

As shown in FIG. 3, the crawler belt 20 includes an endless steel belt21 made of stainless steel (or a thin metal belt or ahigh-tensile-strength belt) and an endless belt main body 22, the beltmain body 22 being made of rubber (or an elastic material) such as SBRand urethane rubber and being attached all around the outer periphery ofthe steel belt 21 by vulcanization bonding, etc.

The steel belt 21 is constructed by welding opposite ends of anelongated thin belt of a plate thickness of from 0.05 to 1.0 millimeters(0.15 millimeters in this embodiment). A width of the steel belt 21 isgenerally same as that of the wheel 10. The steel belt 21 has circularengagement holes 21 a arranged at even intervals (the same interval asthat of the engagement projections 12 a of the wheel 10) in acircumferential direction at a center in the width direction thereof. Adiameter of the engagement holes 21 a is the same as or a slightlygreater than that of the engagement projections 12 a.

The steel belt 21 according to this embodiment is extremely thincompared with a base part 23 (of a thickness of 3 millimeters) to bedescribed later. The thickness of the steel belt 21 is exaggerated indrawings.

As shown in FIGS. 1 and 3, the belt main body 22 integrally includes anendless base part 23 of a width greater than that of the steel belt 21,a shielding flange 24 formed on opposite sides in a width direction ofthe base part 23 and tread lugs 26 spacedly formed on an outer peripheryof the base part 23. The base part 23 has generally semi-sphericalescape recesses 23 a arranged at center in the width direction thereof,at locations corresponding to the engagement holes 21 a of the steelbelt 21 to communicate with the engagement halls 21 a.

The crawler belt 20 is placed around half of the periphery of the wheels10 in the front and rear. As shown in FIG. 4, in an area covering halfof the periphery of the wheel 10, the steel belt 21 contacts the outerperipheral surface of the wheel 10 directly, the engagement projections12 a of the wheel 10 engaging the engagement holes 21 a of the steelbelt 21 and at the same time entering the escape recesses 23 a of thebase part 23.

The shielding flange 24 is formed continuously all around the peripheryof the belt main body 22. The shielding flange 24 extends radiallyinward from the base part 23. The outer surface of the edge of theshielding flange 24 is an inclined surface. By this, the shieldingflange 24 is given a tapered cross section, thereby being allowed to bedeformed easily.

The tread lug 26 extends in a width direction of the crawler belt 20 andhas a trapezoidal longitudinal section. In this embodiment, a thicknessof the tread lug 26 is 5 millimeters in lower base and 3 millimeters inupper base in longitudinal section while its height is 15 millimeters.The tread lug 26 is of an extremely small thickness for its height and,therefore, has a small flexural rigidity. As a result, the tread lug 26is easy to bend when a force in a longitudinal direction of the crawlerbelt 20 is applied. Preferably, the height of the tread lug 26 is notless than 3 times and not greater than 7 times as large as its thickness(an average thickness or a thickness at center in a height direction).More preferably, the height of the tread lug 26 is not less than 3.5times and not greater than 5 times as large as its thickness. If theheight of the tread lug 26 is less than 3 times as large as itsthickness, the flexural rigidity of the tread lug 26 is not smallenough. If the height of the tread lug 26 is greater than 7 times aslarge as its thickness, the tread lug 26 is not strong enough in theheight direction. The tread lug 26 has a planer shape bent at the centeras shown in FIG. 1. The bending adds to the strength of the tread lug 26against load in height direction, i.e. self-weight of the robot. In thisembodiment, as shown in FIG. 6, bending direction of the tread lugs 26is changed every few tread lugs 26.

In a robot of the above mentioned construction, when the actuators ofthe crawler units 2 in the left and right are driven, the crawler belt20 is rotated by rotation of the wheels 10 connected to the actuators.As a result, the robot moves.

Although the belt main body 22 used in the crawler belt 20 is made ofrubber, since it is reinforced with the steel belt 21, it does notstretch even after long use and can be prevented from coming off thewheel 10. Moreover, the crawler belt 20 can be greatly reduced inweight. The first reason is that the crawler belt 20 is reinforced withthe thin steel belt 21 without being increased in thickness. The secondreason is that the belt is engaged with the wheel 10 via the steel belt21, which eliminates the necessity of forming projections for engagingwith the wheel 10 or a sprocket on the belt main body 22 (refer to theabove-mentioned prior art documents).

The crawler belt 20 can be surely prevented from coming off the wheel 10in a left and right direction since the projections 12 a of the wheel 10fit into the engagement holes 21 a of the steel belt 21.

In this embodiment, since flexible tread lugs 26 are provided, the robotcan easily move over relatively low rubble S′ having a flat surface asshown in FIG. 7. It is because the tread lugs 26 are elasticallydeformed and, accordingly, contact area with the rubble S′ is increased.This allows the tread lugs 26 to grip the rubble S′ well withoutslipping, and therefore idle running of the crawler belt 20 can beavoided. This function is very helpful especially when the rubble S′ iswet or sands adhere to the rubble S′. As shown in FIG. 7, the rubble S′can be gripped more securely with the two adjoining tread lugs 26 byreducing interval between adjoining tread lugs 26.

Although the tread lug 26 is easy to bend, it is strong enough and isnot deformed too much against load in height direction, i.e. theself-weight of the robot, which allows the robot to keep movingsmoothly. It is because the tread lug 26 has a bent planer shape, andtherefore has high strength in height direction.

The shielding flange 24 of the belt main body 22 contacts the inclinedsurface 30 c of the side plate 30 at the peripheral edge of the sideplate 30 with the shielding flange being elastically deformed. As aresult, an inner space surrounded by the crawler belt 20 and the pair ofside plates 30 is sealed, thereby preventing foreign substances such aswater, sands and dust from entering into the inner space.

A part of the crawler belt 20 which is placed around half of theperiphery of the wheels 10 is subjected to a force to cause theshielding flange 24 to be waved. But the shielding flange 24 can contactthe peripheral edge of the side plate 30 securely without being wavedbecause the shielding flange 24 is elastically deformed as it contactsthe peripheral edge of the side plates 30.

Manufacturing equipment and a method for manufacturing the crawler belt20 will be described hereinafter. As shown in FIG. 8, the manufacturingequipment comprises a lower mold 70 (or a first mold) and an upper mold80 (or a second mold) that moves up and down with respect to the lowermold 70.

The lower mold 70 includes a base section 71 and a molding section 72having an inverted U-shaped cross-section, which are detachable fromeach other. The lower mold 70 has a hollow rectangular parallelepipedshape with both ends open. As shown in FIG. 9, the molding section 72has receiving holes 72 a arranged at even intervals in a longitudinaldirection on an upper surface thereof. Mold pins 74 are removablyreceived in the receiving holes 72. The mold pin 74 includes a headportion having a semi-spherical shape and being provided as a moldprojection 74 a. A pair of linear auxiliary mold recesses 73 for moldingthe shielding flange 24 are formed sandwiching a row of the moldprojections 74 a on the lower mold 70.

The upper mold 80 has a shape of a rectangular plate. The upper mold 80has a shallow and wide mold recess 81 extending in a longitudinaldirection thereof formed on a lower surface thereof. The upper mold 80also has six lug mold recesses 86 formed therethrough from top tobottom. The lug mold recess 86 has a shape corresponding to that of thetread lug 26.

The steel belt 21 is passed through the hollow lower mold 70 and a partof the steel belt 21 is placed on the upper surface of the lower mold70. At that time, the mold projections 74 a of the lower mold 70 arefitted into the engagement holes 21 a of the steel belt 21, therebypositioning the steel belt 21.

With the steel belt 21 positioned in the above described manner, a rawrubber sheet (elastic material, not shown) containing a vulcanizingagent and of a predetermined length is placed on the upper surface ofthe molding section 72 of the lower mold 70.

Then the upper mold 80 is lowered to press the raw rubber sheet and themolds 70, 80 are heated, thereby vulcanization-bonding(vulcanization-molding) a part 22′ of the belt main body 22 (a partdivided in a circumferential direction of the belt main body 22 to beformed to be endless) to the outer periphery of the steel belt 21 asshown in FIG. 9. It is preferable that primer (adhesive) is applied toan outer peripheral surface of the steel belt 21 beforehand to enhancestrength of adhesion between the part 22′ of the belt main body 22 andthe steel belt 21.

At the time of the molding, a part of the base part 23 is molded withthe mold recess 81, a part of the shielding flange 24 is molded with theauxiliary mold recess 73, the escape recess 23 is molded by allowing themold projection 74 a to press into the rubber material and the tread lug26 is molded by allowing the rubber material to enter the lug moldrecess 86. A part of the rubber material protruded from an upper openingof the lug mold recess 86 is removed with a spatula, etc.

After the molding is done as described above, the upper mold 80 islifted. Then as shown in FIG. 10, the steel belt 21 is peeled off thelower mold 70. Since the molding of the rubber as described aboveinvolves contraction, the mold projection 74 a is attached strongly tothe rubber, and therefore the mold pin 74 is removed from the lower mold70 together with the steel belt 21 and the part 22′ of the belt mainbody 22.

Next, the mold pin 74 is removed from the steel belt 21 and the part 22′of the belt main body 22 as shown in FIG. 11. Since the mold pin 74 isseparate from the lower mold 70, the mold pin 74 can be easily detachedfrom the escape recess 23 a of the part 22′. The productivity isimproved compared to a case where mold projections are integrally formedwith the lower mold.

Next, a new part of the steel belt 21 is positioned on the lower mold70, the new part adjoining the part to which the part 22′ of the beltmain body 22 is vulcanization-bonded, by moving the steel belt 21 in acircumferential direction, and another part 22′ of the belt main body 22is molded in the foregoing way. By repeating the procedure, the beltmain body 22 can be attached to the entire periphery of the steel belt21. The part 22′ of the belt main body 22 newly molded is madecontinuous to the previously molded part 22′, thereby making theadjoining parts 22′ of the belt main body 22 substantially integral witheach other. According to this method, the crawler belt 20 including theshielding flange 24 and the tread lug 26 can be manufacturedinexpensively by using the lower mold 70 and the upper mold 80, both ofsimple construction, without using a split mold.

Other embodiments of the present invention are described below referringto FIGS. 12 to 17. Same numbers are used for the componentscorresponding to those of the first embodiment and a detaileddescription thereof is omitted.

In a second embodiment as shown in FIG. 12, an outer peripheral surfaceof the wheel 10 is a generally-cylindrical surface. To be more specific,the outer edge of the cross section of the wheel has a crowned shape ofa large radius of curvature with a central part elevated from oppositeends. In other words, outer diameter of the wheel 10 is graduallyreduced as it goes from a center toward opposite ends in a widthdirection. Although exaggerated in the drawings, the difference betweenthe diameters at the center and at the both ends of the wheel 10 is, infact, not substantial: the diameter at the center is 100 millimeters andthe diameter at the both ends is smaller than that by 0.3 millimeters inthe wheel 10 having a width of 30 millimeters in this embodiment.

A third embodiment as shown in FIG. 13 is identical to the secondembodiment except the following: the steel belt 21 is embedded in thebase part 23 of the belt main body 22 and a thin rubber layer 29 isformed on an inner periphery of the steel belt 21. The rubber layer 29has an inner-peripheral surface corresponding to the outer peripheralsurface of the wheel 10. When the wheel 10 is made of metal, the rubberlayer 29 serves to prevent abrasion caused by metal-to-metal contactbetween the steel belt 21 and the wheel 10.

In a fourth embodiment as shown in FIGS. 14 to 16, the wheel 10 is madeof resin, etc. and its outer peripheral surface is a cylindricalsurface. Engagement pins 12 made of metal are embedded and arranged ateven intervals in a circumferential direction at a center in the widthdirection of the outer peripheral surface of the wheel 10. A head partof the engagement pin 12 having a semi-spherical shape projects from theouter peripheral surface of the wheel 10 and is provided as anengagement projection 12 a.

A shielding flange 24′ is formed continuously all around periphery ofthe belt main body 22 and projects in an oblique direction from an outerperipheral surface of the base part 23. The shielding flange 24′ has atapered cross-section and is easy to be elastically deformed.

As shown in FIG. 16, the side plate 30 comprises a metal plate 31 and apair of seal members 32. As shown in FIG. 15, the metal plate 31 has afront and rear end edges 31 a, each having a semi-circular shapecorresponding to a shape of a peripheral edge of the front and rearwheels 10, respectively. The front and rear end edges 31 a are, as shownin FIG. 15, cut away from inside to be reduced in thickness.

As shown in FIG. 16, the seal member 32 is detachably attached to anupper and lower parts of the peripheral edges of the metal plate 31, theupper and lower parts having a linear shape. To be more specific, theseal member 32 is made of rubber material having smaller elasticcoefficient than the belt main body 22 of the crawler belt 20 to bedescribed later. The seal member 32 is attached to a bracket 33 having alinear shape with a L-shaped cross section by vulcanization bonding,etc. and the bracket 33 is removably fixed to upper and lower parts ofthe peripheral edge of the side plate 30 with a screw 34. The sealmember 32 includes a thin raised wall 32 a.

In the part of the crawler belt 20 which is placed around the wheels 10in the front and rear, the edge of the shielding flange 24 contacts theend edges 31 a in the front and rear of the side plate 30. In the otherpart of the crawler belt 20 which is placed between the wheels 10 in thefront and rear, the edge of the shielding flange 24′ contacts the raisedwall 32 a of the seal member 32. As a result, the inner space surroundedby the crawler belt 20 and the pair of side plates 30 is sealed, therebypreventing foreign substances such as water, sands and dust fromentering into the inner space.

In the part of the crawler belt 20 which is placed around half of theperiphery of the wheels 10, the crawler belt 20 is bent, and therefore,the shielding flange 24′ is warped away from the end edge 31 a of theside plate 30. But the edge of the shielding flange 24′ can contact theend edge 31 a securely despite the warping because the edge of theshielding flange 24′ is elastically deformed as it contacts the end edge31 a of the side plate 30. When the shielding flange 24′ of the crawlerbelt 20 contacts the seal member 32 at the upper and lower parts of theperipheral edge of the side plate 30, the seal member 32 is deformedmore greatly than the shielding flange 24′ because the seal member 32has smaller elastic coefficient and is thinner than the shielding flange24′. This permits the seal member 32 and the shielding flange 24′ to bemaintained in contact with each other even when the crawler belt 20flaps in an area not restrained by the wheels 10 because the seal member32 is deformed following the flapping of the belt 20. The seal member 32is coated with Teflon®, etc., which serves to reduce friction betweenthe seal member 32 and the shielding flange 24′.

The lower mold 70 and the upper mold 80 as shown in FIG. 17 are used tomold the crawler belt 20 according to the fourth embodiment of thepresent invention. In this embodiment, a pair of auxiliary mold recesses82 having a linear shape are formed along opposite sides of the moldrecess 81 of the upper mold 80. The auxiliary mold recess 82 has across-section corresponding to the shield flange 24′. The molds 70 and80 are used in the same manner as in the first embodiment as describedabove.

The present invention is not limited to the above embodiments, butvarious modifications can be made without departing from the scope ofthe invention. For example, the pair of crawler units may be driven byboth of front and rear wheels. Another wheel may be deployed between thewheels in the front and rear. A trailing wheel may not be engaged withthe crawler belt as far as it restricts movements of the crawler belt inthe width direction.

The tread lug 26 may have a planer shape of a wave being bent at aplurality of points. The tread lug 26 according to the first and secondembodiments may not have a trapezoidal longitudinal section but may beformed with a uniform thickness. Two rows of short helical engagementprojections running in different directions (double helical) may beformed on the wheel 10 and engagement holes corresponding to the helicalengagement projections may be formed in the high-tensile-strength beltso that the crawler belt is surely prevented from meandering.

The entire periphery of the belt main body may be molded at one time byinsert injection molding, etc. The actuator may not be an electric motorbut a hydraulic motor or an engine. Application of the crawler unitaccording to the present invention is not limited to the rescue robots.It may be applied to other light weight robots such as those used forcleaning hospitals or may be applied to light construction machinesother than robots.

1. A crawler belt comprising an endless high-tensile-strength belt and abelt main body made of elastic material and attached to an outerperiphery of said high-tensile-strength belt, said high-tensile-strengthbelt having engagement holes arranged at even intervals in acircumferential direction thereof, said engagement holes to engage withengagement projections of a wheel, said belt main body integrallyincluding an endless base part attached all around an outer periphery ofsaid high-tensile-strength belt and a plurality of tread lugs formedspacedly on an outer periphery of said base part, wherein an innerperiphery of said base part is completely contacting the entire outerperiphery of said high-tensile-strength belt, said base part coveringsaid engagement holes and having escape recesses formed at locationscorresponding to said engagement holes of said high-tensile-strengthbelt, said escape recesses to receive said engagement projections ofsaid wheel.
 2. A crawler unit comprising a plurality of wheels disposedseparately in a front and rear direction and a crawler belt trainedabout said wheels, wherein said crawler belt comprises an endlesshigh-tensile-strength belt and a belt main body made of elastic materialand attached to an outer periphery of said high-tensile-strength belt,said high-tensile-strength belt having engagement holes arranged at evenintervals in a circumferential direction thereof, said belt main bodyintegrally including an endless base part attached all around said outerperiphery of said high-tensile-strength belt and a plurality of treadlugs formed spacedly on an outer periphery of said base part, wherein aninner periphery of said base part is completely contacting the entireouter periphery of said high-tensile-strength belt, said base partcovering said engagement holes and having escape recesses formed atlocations corresponding to said engagement holes of saidhigh-tensile-strength belt, and wherein a driving wheel of saidplurality of wheels has engagement projections arranged at evenintervals in a circumferential direction on an outer peripheral surfacethereof, said engagement projections being adapted to be engaged withsaid engagement holes of said high-tensile-strength belt of said crawlerbelt and at the same time to enter said escape recesses of said beltmain body.
 3. A crawler unit according to claim 2, wherein outerperipheral surfaces of said plurality of wheels are generallycylindrical surfaces.
 4. A crawler unit according to claim 3, whereinsaid engagement holes of said high-tensile-strength belt have agenerally circular shape, said engagement projections of said wheel havea generally semi-spherical shape and said escape recesses of said basepart have a generally semi-spherical shape.
 5. A crawler unit accordingto claim 2, wherein said crawler unit further comprises a pair of sideplates extending in a front and rear direction to cover opposite sidesurfaces of said plurality of wheels, said belt main body comprisingshielding flanges continuously formed along an entire length on oppositesides of said base part, edges of said shielding flanges contactingperipheral edges of said side plates.
 6. A crawler unit according toclaim 2, wherein said tread lugs extend in a width direction of saidbase part, said tread lugs having a planar shape bent at least at onepoint, the height of said tread lugs being not less than 3 times and notgreater than 7 times as large as the thickness of said thread lugs.
 7. Acrawler belt according to claim 1, wherein said belt main body isattached only to the outer periphery of the high-tensile-strength belt.8. A crawler belt according to claim 7, wherein thehigh-tensile-strength belt is composed of a steel belt.
 9. A crawlerunit according to claim 2, wherein the high-tensile-strength beltdirectly contacts the outer peripheral surface of the wheel.